DE3531576C2 - Electrosurgery generator - Google Patents

Description

The invention relates to an electrosurgical generator the type specified in the preamble of claim 1.

Such an electrosurgery generator is known from DE 28 03 017 A1 which will be discussed in more detail below.

By using an electrosurgical generator during an operation, the surgeon is able to simply cut or cut with hemostasis or purely coagulate. The surgeon can do that quickly select and change different operating modes, while the operation is going on. In every operating mode it is important to regulate the electrical power, which is delivered to the patient to the desired to achieve surgical effect. When more power is supplied  is considered necessary, there is an unnecessary one Tissue destruction, and the healing process is prolonged. If less than the desired electrical output surgery is usually hampered. Different types of fabrics are progressing Operation encountered, and each different Tissue will usually perform more or less require, because of a change in the impedance of the fabric. Accordingly, all successful species of electrosurgical generators of any kind Power regulation is used to achieve the desired by the surgeon to control electrosurgical effects.

There are two types of power control in known electrosurgical generators common. The most common type is controlled the DC power consumption of the generator. With this type of power control, the size of power limited from the conventional AC grid to which the generator is connected is. A feedback loop compares them through the actual supply supplied with a target power setting, to achieve the regulation. On Another type of power control in known electrosurgical generators involves controlling the gain of the RF amplifier. A feedback loop compares the output power delivered by the RF amplifier a target power value and the gain is corresponding set.

Both known types of power control have achieved some success, yet they exhibit certain undesirable Properties on. An undesirable property concerns the response time for the control. The impedance of the various tissues encountered during surgery can fluctuate considerably. When moving  the active electrode connected to the output of the surgical generator from a high impedance fabric to a lower fabric Impedance can make the low impedance tissue unnecessary be destroyed or damaged before the surgical generator reduce the output power to a value can be compatible with the low impedance fabric is. Likewise, if a tissue is found to have high impedance the output power of the generator is temporary are not sufficient to determine the exact surgical effect the surgeon wishes to evoke or continue. The Accurate execution of the operation becomes difficult or impossible.

Furthermore, the power control in known Electrosurgical generators made them large in size, because these known generators are designed so that the maximum power transmission in medium impedance ranges is achieved. Like any amplifier, it becomes an electrosurgical generator the maximum power transfer reach if its internal impedance is equal to the output load impedance to which the generator is connected. At high impedances will affect performance due to the difference in the load impedance is reduced compared to the internal impedance. To compensate for this, the surgeon increases the power setting to a value higher than necessary is. Once the cut through the tissue high impedance goes through, the output power is too large and result yourself tissue destruction or unwanted surgical Effects. This is the case, for example, when making the initial cut. The skin contains a relatively large percentage on dead cells as well as on cells that are considerably less Moisture than other cells in tissues below the Skin contain what their impedance compared to the impedance of the tissue under the skin enlarged. A higher one Power setting is therefore for the initial cut required. However, once the cut has been made  less power is required. In typical known electrosurgical generators the initial cut was deeper than desired because of the active Electrode, d. H. the electrosurgical instrument because of the oversized value of the delivered service penetrated deeper, when the surgeon asked. The surgeon usually wants to check the depth of cut and the operation Execute at controlled depths. If the power regulation is not reliable, a deeper cut in certain areas of unwanted bleeding or other unwanted Effects of the operation. That's the Reason why most surgeons generally prefer the initial cut with a conventional scalpel instead of using the active electrode of an electrosurgical generator.

Another related to the power regulation The problem with known electrosurgical generators is arcing at idle immediately before the start of surgical procedure. Before the surgical procedure starts, the electrosurgery generator does not perform due to the idle state from. The power control circuit tries to compensate for that by having a state of maximum power output generated. Once the active electrode in certain Distance is brought from the tissue, it happens due to the relatively high voltage caused by the Power control circuit set maximum power state is present for an immediate Electric arc. The constant arcing is true desired in the coagulation or fulguration mode, however, it is undesirable in other modes. The power control circuit compensates later the excessive performance and reduced it. Still caused the initial arcing  usually excessive tissue destruction and other undesirable tissue effects. For arcing and excessive tissue destruction can occur at any time when the surgeon moves the active electrode to the tissue.

Idle states or states of excessively high output impedance also increase the patient's risk of stray capacitance Burns. The are burns that are generated by electricity, which from the patient to any surrounding grounded, electrically conductive object such as the operating table flows instead of over the patient plate, d. H. the inactive Return electrode to the electrosurgery generator. Such Burns are usually caused by RF leakage currents caused by the surgical signal and due to the stray capacities between the Patient and an adjacent grounded object flow. Decreasing the output voltage when idle or in the high impedance state reduces the size and possibility of such RF leakage currents.

Another problem associated with power control in known electrosurgical generators refers to shorting the generator output terminals. The human nature brings with it a common, albeit not recommended technique for quick determination, whether an electrosurgery generator is functional consists of simply short-circuiting the two output electrodes and watching an electrical spark. A not The unusual result of this short-circuiting is the destruction the power supply in the generator. The generator is forced to try quickly from an idle state high power to a short circuit condition lower Regulate impedance. Because of the limitations of the rules the electrical power components of the  Power supply usually overdriven and quickly destroyed, before the compensation can take place.

In the electrosurgery generator known from DE 28 03 017 A1 the error signal, which is obtained by comparing the Actual output power signal with the target output power signal is generated, used to amplify the output stage connected power amplifier. The Voltage signal and the current signal necessary for the formation of the Actual output power signals are used are mean values the peak values of the voltage or the current and formed by an integration circuit. These mean signals stand, since they do not occur simultaneously, not in linear Relationship to the actual output power associated with the surgery signal high frequency is delivered. To compensate for this Non-linearity is in the known electrosurgery generator a compensating circuit is required, which the performance at the top and lower end of the power range increased so Allow delivery of a constant output power. These The type of power control is therefore not faster than that of the other known electrosurgery generators described above and in particular also includes no possibility rapid impedance changes in the load on the electrosurgical generator to compensate.

DE 26 19 081 A1 describes a pulse control circuit for an electrosurgery generator and a method of control the average power of its pulse-modulated output signals. The pulse modulation is only for setting the duty cycle of the output signals to the with to adapt this energy to the special surgical purpose. The electrosurgery generator is either cut or coagulate or cut and coagulate at the same time, depending on the duty cycle of its output signal. A high duty cycle is used for cutting and coagulation with low duty cycle. Even a very low one Duty cycle is because of the typical surgical output signal  has a frequency in the range of 500 to 750 kHz, include hundreds of vibrations. The well-known electrosurgery generator is therefore unable to change impedance its load faster than the other known ones Electrosurgical generators to be considered in a regulation.

DE 32 25 221 A1 describes an electrosurgical generator, with different output stages depending on the type of the desired surgical procedure can be chosen.

DE 33 40 891 A1 deals with a circuit arrangement for pulse width control of a clocked power supply unit, which in particular for the power supply of a high-frequency Power stage of an electrosurgical generator can be used. The design of this high-frequency power amplifier itself is in DE 33 40 891 A1 not addressed.

The object of the invention is in an electrosurgical generator the type specified in the preamble of claim 1 Regulate the output power so that the electrosurgical generator gets a faster response time so a better and constant power control itself Relatively high and low impedance loads result and also limit the output current and the output voltage let to problems like arcing, by stray capacitance caused burns and destructive short-circuit currents to avoid.

This object is achieved by the in claim 1 specified features solved.

In the electrosurgical generator according to the invention, each Vibration of the surgical signal it emits in the energy content regulated by the time width of the driver pulses is modulated, which generate each oscillation of the surgical signal. The width of each driver pulse is dependent the difference between the actual output power signal and  modulated the target output power signal to thereby output Bring performance to the target performance value. Because everyone Vibration of the surgery signal is regulated, the power regulation in the electrosurgery generator according to the invention respond very quickly. With target output power values, which are lower than the maximum possible target output power values of the electrosurgery generator, the power is regulated reliable even when the electrosurgery generator loaded with tissue of relatively high impedance is. The surgeon can perform the operation while it is in progress goes more precisely and precisely because of undesirable effects caused by changes in tissue impedance, significantly reduced or be eliminated. The one used according to the invention Pulse width modulation technology is used for power control higher load impedances more effective than the known power control techniques.

The one used in the electrosurgical generator according to the invention Pulse width modulation power control technology permitted thus, the energy content of each vibration of the sinusoidal To regulate the surgical signal that is fed to the patient. This results in very precise power control, which moreover, very fast response times enables a strong to achieve improved constant power control when the tissue impedance fluctuates quickly. Superior and greatly improved surgical operational effects arise. The constant power control, the relative due to that even with tissues high impedance is available represents a significant improvement in the field of electrosurgery.

Finally, with the electrosurgery generator after the Invention whose size and weight can be reduced and also the cost of the power supply can be reduced. A Power supply at a lower cost, with fewer components, with smaller size and lower weight results with the but still a sufficient level of gross performance control can be achieved in the power supply because of the pulse width modulation technology the final one in the power control circuit  precise power control can take place.

The objects form advantageous embodiments of the invention of subclaims.

More precise sensing signals can be achieved in that the Current and voltage are recorded directly at the output stage so that shortcomings in circuit elements such as the power amplifier and the power transformer are taken into account will.

In a further embodiment of the invention, a voltage or Current limit signal instead of the current sensing signal or voltage sensing signal used to the maximum output current of the electrosurgical generator at relatively low impedances or the maximum output voltage of the electrosurgical generator at relative limit high impedances. Limiting the maximum Output voltage at relatively high impedances helps to avoid unwanted Avoid arcing and the beneficial to achieve surgical effects on the tissue and the risk of reduce burns caused by stray capacities. Limiting the maximum output current at relatively low ones Impedances help prevent high currents, even if that Output electrodes of the electrosurgical generator short-circuited will.

Embodiments of the invention are described below Described in more detail with reference to the drawings. It shows

Fig. 1 is a block diagram of the electrosurgical generator according to the invention,

Fig. 2 is an expanded diagram of certain portions of Fig. 1,

Fig. 3 is an expanded diagram of certain portions of Fig. 1,

FIGS. 4A-4M are diagrams of signals present at certain points in the results shown in Figs. 1 and 3 circuit diagrams,

Fig. 5 is a diagram in which the output signal surgical output power over the output (fabric) - impedance is plotted in the form of power control curves, which are obtained by the circuit of Figure 2.

FIG. 6 is a graph plotting the output surgery signal output versus the output (tissue) impedance of the electrosurgical generator with modifications made to a portion of the circuit shown in FIG. 2; and

Fig. 7 is a circuit diagram of a circuit which replaces part of a circuit shown in Fig. 2.

A preferred embodiment of an electrosurgical generator is shown in FIG. 1 and is designated overall by reference number 10 . A control panel 12 as part of a setpoint generator of generator 10 has the typical switches and other control devices for controlling the operating mode of generator 10 and for setting the setpoint of the power to be output in each operating mode. In addition, the control panel 12 can have devices for setting the performance values for cutting and / or hemostasis. AC power is supplied to generator 10 from a conventional AC power line 14 . A controllable direct current supply 16 converts the alternating current from line 14 into direct current at a point 20 . An output power control signal is supplied to a location 18 of the control panel 12 to the DC power output of the power supply to control 16 at the point 20 corresponding to the value of the set target power and to limit total. The output power of the power supply 16 is fed to a power amplifier 22 at point 20 . The power amplifier 22 converts the direct current power at the point 20 into a periodic, pulse-width-modulated signal in the form of driver pulses 24 . A power transformer 26 as part of an output stage receives the pulse width modulated signal in the form of driver pulses 24 and converts it into a pulse width modulated AC signal 28 .

The pulse width modulated alternating current signal 28 is applied to a bandpass filter 30 , which represents a further part of the output stage and has a bandpass characteristic only at the predetermined high frequency of a surgery signal 32 supplied by the generator 10 . The surgical signal 32 generates the surgical effect, ie it serves to carry out an operation. The frequency of the surgical signal 32 is sufficiently high to avoid nerve stimulation and is, for example, 500 kHz. The bandpass filter 30 eliminates any higher order harmonics generated by the power amplifier 22 or transformer 26 to reduce the risk of stray burns to the patient. The bandpass filter 30 also prevents the presence of circulating direct currents generated by tissue rectification effects. The bandpass filter 30 converts the AC signal 28 into a sine wave due to the effects of the passive dummy elements of the filter. Surgical signal 32 is applied to a conductor connected to the active electrode used by the surgeon. A conductor 34 is the reference potential conductor for the surgical signal 32 and is connected to the patient plate or inactive electrode on which the patient is arranged.

When using a bipolar electrosurgical instrument both conductors are connected to the instrument. Output isolation capacitors, not shown, can be arranged in the two conductors to likewise block circulating direct currents.

A current sensor 36 is connected in series in which the surgery signal carrying conductor 32, for providing a sensed-current signal 38, which is related to the instantaneous magnitude of current flowing in the conductor. A voltage sensor 40 is connected between this conductor and the conductor 34 and is used to obtain a voltage sensing signal 42 which represents the instantaneous voltage that is present between the two conductors. Accordingly, both the instantaneous output current and the instantaneous output voltage of the surgical signal 32 are sensed in the generator 10 where the surgical signal is delivered, namely at the output of the output stage 26 , 30 . This provides an accurate indication of the magnitude of the instantaneous output current and voltage applied to the tissue.

In order to regulate the output power of the electrosurgery generator 10 , which is output with the surgery signal 32 , the current and voltage sensing signals 38 and 42 are applied to RMS / DC converter circuits 44 and 46 , respectively. The converter circuits 44 and 46 each convert the sensing signals to an RMS value, which is represented by a DC output signal. Accordingly, an RMS current sensing signal 48 is a DC signal that represents the RMS value of the instantaneous output current of the surgery signal 32 , and an RMS voltage sensing signal 50 is a DC signal that represents the RMS value of the instantaneous output voltage of the surgery signal 32 applied to the patient. Converting the instantaneous current and voltage sense signals to RMS provides a true and accurate representation of the magnitude of the current and voltage that are actually provided with the surgery signal 32 .

The RMS current sensing signal 48 is applied to a current limiting circuit 52 and the RMS voltage sensing signal 50 is applied to a voltage limiting circuit 54 . Current limit and voltage limit signals 56 and 58 are applied to the limiting circuits 52 and 54 from a scaling circuit 60 . The scaling circuit 60 is controlled by an operating mode logic circuit 62 , which outputs scaling control signals 64 to the scaling circuit 60 . The scaling circuit 60 is also controlled by a target power signal 66 provided by the control panel 12 . The mode logic circuit 62 is controlled by mode control signals 65 which are applied by the control panel 12 . The operating mode control signals 65 determine the operating mode of the generator 10 . The mode logic circuit 62 also provides a control signal 67 to the power supply 16 that controls the amount of DC power at 20 according to the selected mode.

The size of the current limit signal 56 and the size of the voltage limit signal 58 are determined by the operating mode of the generator 10 and by the size of the target power signal 66 . The current limit signal 56 represents a minimum amount of current that should be supplied to high impedances and causes the maximum voltage of the surgical signal 32 applied to high impedances to be limited. The voltage limit signal 58 represents the minimum magnitude of the output voltage that should be applied to low impedances and causes the maximum current of the surgery signal 32 applied to low impedances to be limited.

The limiting circuit 52 compares the current limit signal 56 with the signal 48 , which represents the instantaneous magnitude of the current that is supplied with the surgery signal 32 . As long as the RMS current sensing signal 48 exceeds the current limit signal 56 , the current limiting circuit 52 provides a current output signal 68 which corresponds to the RMS current sensing signal 48 . Likewise, the limiting circuit 54 compares the voltage limit signal 58 with the effective voltage sensing signal 50 , which represents the instantaneous voltage of the surgery signal 32 . As long as the RMS voltage sensing signal 50 exceeds the voltage limit signal 58 , a voltage output signal 70 is present which corresponds to the RMS voltage sensing signal 50 . Should either the RMS current sense signal 48 or RMS voltage sense signal 50 fall below the values of signals 56 or 58 , the current limit signal 56 or the voltage limit signal 58 is clamped and supplied as the current output signal 68 or as the voltage output signal 70 . Accordingly, the current delivery signal 68 is either the RMS current sensing signal 48 or the current limit signal 56 , whichever is greater. Likewise, the voltage output signal 70 is either the RMS voltage sensing signal 50 or the voltage limit signal 58 , whichever is the larger. Limiting the current output signal 68 to a value that is not less than the current limit signal 56 causes the output voltage of the surgical signal 32 to be maintained at a predetermined maximum value at high impedances. Limiting the voltage output signal 70 to the minimum magnitude defined by the voltage limit signal 58 causes the output current of the surgical signal 32 to be limited to a predetermined and safe maximum value at low impedances.

A signal representing the actual output power, ie the delivered power, is generated by an analog multiplier 72 , in which the current output signal 68 and the voltage output signal 70 are multiplied. The multiplier 72 supplies an actual output power signal 74 .

The scaling circuit 60 also provides a signal 76 which represents a desired output power value of the surgery signal 32 . The scaling circuit 60 sets the target output power signal 76 according to the target power signal 66 from the control panel 12 and according to the scaling control signals 64 provided by the mode logic circuit 62 according to the selected mode.

The desired output power signal 76 and the actual output power signal 74 are compared with one another in a comparator 78 in the form of a differential amplifier, and an error signal 80 is supplied. The error signal 80 represents the difference in size between the actual output power and the target output power. A pulse width modulation circuit 82 receives the error signal 80 and uses it to generate a pulse width control signal 84 .

A driver circuit 86 designed as an amplifier receives the pulse width control signal 84 and generates a driver signal 90 . The drive signal 90 consists of a series of drive pulses which are supplied at a predetermined frequency in order to determine the predetermined frequency of the surgical signal 32 . The width or duration of each driver pulse is controlled by the pulse width control signal 84 . The driver signal 90 controls the operation of the power amplifier 22 . Each driver pulse defines the width and thus the energy content of each driver pulse 24 , ie the pulse width modulated signal from the power amplifier 22 . The width of each driver pulse 24 defines the output power in each oscillation of the surgical signal 32 . Thus, the output power is ultimately controlled by the pulse width control signal 84 .

A duty cycle generator 92 is controlled by a signal 94 from the mode logic circuit 62 . A duty cycle signal 96 from the duty cycle generator 92 also controls the driver circuit 86 . Duty cycle operation is typically established in the modes of operation of the hemostatic cutting and coagulation generator 10 . The duty cycle signal 96 causes the driver circuit 86 to control the output of the pulses in the drive signal 90 in a periodic duty cycle according to the mode. In the cutting mode, the surgery signal 32 is a continuous sine wave and the duty cycle generator 92 is out of order. A synchronizing or oscillator signal 98 is provided by the driver circuit 86 to cause the pulse width modulation circuit 82 to respond in synchronism with the same frequency as that of the driver pulses of the driver signal 90 .

The pulse width control signal 84 is obtained by comparing the actual output power signal 74 with the target output power signal 76 . Slight fluctuations in the output value at 20 of the controllable direct current supply 16 become largely insignificant because the power is regulated by pulse width modulation.

Details of the RMS / DC converter circuits 44 and 46 , the limiting circuits 52 and 54 , the multiplier 72 , the comparator 78 and the scaling circuit 60 are shown in FIG. 2, to which reference is now made.

The target power signal 66 is obtained by setting a potentiometer (not shown) on the control panel 12 ( FIG. 1). The target power signal 66 is a voltage signal that represents the target power value. The target power signal 66 is used to generate the current limit signal 56 which is applied to the limiting circuit 52 . The current limit signal 56 is generated by applying the target power signal 66 to an operational amplifier 100 . A square root circuit 102 is connected between the output terminal of the operational amplifier 100 and its input terminal which receives the target power signal 66 . The output signal 104 of the operational amplifier 100 generally represents the square root of the target power signal 66. The square root of the target power signal 66 is desirable because the current limit signal 56 limits the output voltage of the surgical signal 32 to a maximum constant value at high impedances. The output voltage of the surgical signal 32 is related to the output power by a quadratic function when a certain impedance or resistance is loaded, and therefore the output power is related to the output voltage by a square root function. Because the target power signal 66 represents power, its square root for a load of certain impedance or resistance relates to the output voltage of the surgical signal 32 . The output signal 104 is therefore a nonlinear square root function of the target power signal 66 .

A scaling function is performed on the output signal 104 by an analog switch 106 and a resistance divider circuit. The scaling control signals 64 from the mode logic circuit 62 ( FIG. 1) optionally control the analog switch 106 of the scaling circuit 60 . The scaling control signals 64 consist of several individual signals, but each is referred to as a scaling control signal 64 to simplify the description. When a scaling control signal 64 is applied, one of the switches 106 A or 106 B is closed and a voltage divider circuit is established between one of the resistors 108 or 110 and the resistor 112 . The switch 106 A or 106 B that is closed depends on the mode of operation of the electrosurgery generator 10 that is selected by the surgeon. To simplify the description, only two different scaling functions are achieved with the analog switch 106 , although in reality a larger number is available according to at least three different operating modes of the electrosurgery generator. The size of the limit signal is determined by the resistance divider circuit.

The current limit signal 56 , which limits the maximum output voltage of the surgical signal 32 , is applied to the positive input of a precision clamping circuit 114 of the limiting circuit 52 . The RMS current sense signal 48 is applied to the negative input of clamp 114 . As long as the RMS current sensing signal 48 exceeds the current limit signal 56 , the RMS current sensing signal 48 is present as the current delivery signal 68 . However, should the RMS current sense signal 48 drop below the current limit signal 56 , the clamp circuit 114 provides the current limit signal as the current output signal 68 . Therefore, although the electrosurgery generator 10 can actually deliver less than the predetermined minimum current in the surgery signal 32 , the power control circuit provides the minimum current. The maximum output voltage of the surgical signal 32 is limited accordingly. The effect is that the actual output of the electrosurgical generator 10 at high impedances decreases because the power control circuit operates on the artificial basis of constant output current delivery at high impedances because of the introduction of the current limit signal 56 into the power calculation in the multiplier 72 instead of the effective current sensing signal 48 .

Examples of the reduction in actual power in the surgical signal 32 from the electrosurgical generator 10 at high impedances by using a minimum current limit signal related to the square root of the target power signal 66 or the value of the target power are as curves 5 A, 5 B, 5 C and 5 D shown in FIG. 5. The four curves 5 A, 5 B, 5 C and 5 D represent selected target power settings for the electrosurgery generator of 100%, 75%, 50% and 25%. The curve 5 A therefore represents the maximum desired output power of the electrosurgery generator 10 Extracting the current limit signal 56 from the square root of the target power signal 66 , as described with reference to FIG. 2, the decrease in the power control capacity for each target power value occurs approximately at the same predetermined relatively high impedance, denoted ZH in FIG. 5, and although non-linear, overall like the non-linear decrease in power at maximum power output.

For many uses, it is desirable to avoid high impedance degradation when the electrosurgical generator 10 is operating at less than its maximum target power. To avoid the decrease in power shown in FIG. 5 at the high impedances when the generator 10 is operating at less than its maximum output power value, the current limit signal 56 is not generated. Instead, the RMS current sense signal 48 is directly applied to the multiplier 72 as the current output signal 68 . The power control curves 6 A, 6 B, 6 C and 6 D, which are shown in Fig. 6, result in this case. The curve 6 A represents the maximum power output of the electrosurgical generator 10 and essentially corresponds to the curve 5 A in FIG. 5. Curves 6 B, 6 C and 6 D represent the power output at 75%, 50% and 25% of the maximum power output. At less than the maximum power output, constant or regulated power is output at impedances that are greater than the impedance ZH. Regulated power is delivered until the maximum output power of the electrosurgical generator is reached, that is, if curves 6 B, 6 C or 6 D intersect curve 6 A, at which point the power decrease takes place because the self-maximum power generation capacity has been reached.

In some other cases, it is desirable to use the limiting circuit 52 to generate the current limit signal 56 , but to modify the value and relationship of the current limit signal to other signals and operational restrictions of the electrosurgical generator 10 . For example, it may be desirable to limit the maximum output voltage of the surgical signal 32 in order to prevent or reduce arcing and the risk of burns caused by stray capacities, but still to achieve constant power control on high impedance tissues. A circuit portion shown in FIG. 7 is an example of a circuit that will generate a constant current limit signal 56 . The operational amplifier 100 and the square root circuit 102 of FIG. 2 are eliminated and the circuit part shown in FIG. 7 is used in their place. Signal 104 is directly connected to a constant positive circuit voltage. The resistance circuit, which consists of resistors 108 , 110 and 112 , and the optional closing of one of the switches 106 A or 106 B determine the current limit signal 56 . An example of a circuit that generates a limit signal that changes linearly with respect to another variable signal is illustrated by the following description of the voltage limit circuit 54 , and the same principle can be applied to the generation of minimum current limit signals.

Various types of current limit signals 56 have thus been described. A minimum current limit signal which changes in a non-linear relationship (e.g. according to a square root relationship) to a variable signal (e.g. the target power signal 66 ) is taken from the circuit part shown in FIG. 2. A constant minimum current signal regardless of the power setting is taken from the circuit part shown in FIG. 7. A linearly changing minimum current limit signal is illustrated by the following description of the removal of the voltage limit signal 58 . These examples show that circuits for generating specially tailored minimum current limit signals are possible. These circuits could regulate the power output at less than the maximum power settings to suit particular types of surgical procedures if it should be determined that the particular types of surgical procedures require specially tailored power control curves at particular impedances.

In order to achieve the desired output power signal 76 as shown in FIG. 2, the desired power signal 66 is scaled by means of an analog switch 116 , which is controlled by the scaling control signals 64 , in accordance with the selected operating mode. Closing switch 116 A causes the full set power signal to be applied to operational amplifier 118 , which serves as a buffer. The target output power signal 76 coincides with the target power signal 66 under these circumstances. Closing the switch 116 B defines a voltage divider circuit consisting of resistors 120 and 122, and to reduce the size of the Solleistungssignals 66 to cause the target output signal corresponds to 76 this reduced value.

The voltage limit signal 58 is taken from the target output signal 76 . The desired output power signal 76 is optionally switched to a voltage divider circuit made up of resistors 124 , 126 and 128 by an analog switch 130 of the scaling circuit 60 . The switches 130 A and 130 B are selectively controlled by the scaling control signals 64 . The minimum voltage limit signal 58 , which controls the maximum output current of the surgical signal 32 , is linearly related to the desired output power signal 76 because of the voltage divider circuit.

An operational amplifier 132 serves as a precision clamping circuit in the limiting circuit 54 . The voltage limit signal 58 is applied to the positive terminal of the operational amplifier 132 and the RMS voltage sensing signal 50 is applied to the negative terminal. As long as the RMS voltage sensing signal 50 is greater than the voltage limit signal 58 , the RMS voltage sensing signal is provided as the voltage output signal 70 . However, should the RMS voltage sensing signal 50 drop below the voltage limit signal 58 , the voltage limit signal is provided as the voltage output signal 70 .

By introducing the voltage limit signal 58 as an artificial replacement for the RMS voltage sensing signal 50 , the maximum output current of the surgical signal 32 is limited to a maximum value, although the output impedance can actually be so low that a much larger output current should flow out of the electrosurgical generator 10 . A minimum voltage value signal is defined for each target output power value, which is linearly related to this target output power value. Because the voltage limit signal 58 defines this constant maximum output current of the surgical signal 32 that the electrosurgical generator 10 will deliver to low impedances, the voltage limit signal and the desired output power signal 76 are in a linear relationship to one another. The output current is limited to a predetermined maximum value at all low impedances regardless of the power settings. This can be understood by referring to the low impedance areas of the diagrams in Figs . The output power of the electrosurgery generator 10 increases approximately linearly as the impedance in the low impedance range (to ZL) increases due to the constant maximum value that the low impedance current due to the introduction of the artificial voltage limit signal 58 relates to the desired output power value stands, can achieve. Limiting the maximum output current prevents, among other advantages, the internal destruction of circuit elements of the electrosurgery generator 10 .

The current and voltage output signals 68 and 70 are applied to the input terminals of the multiplier 72 , as shown in FIG. 2. These signals are multiplied together and the product signal is applied as an actual output power signal 74 to the positive input terminal of the comparator 78 . The target output power signal 76 is applied to the negative input terminal of the comparator 78 through a resistance circuit. The comparator 78 supplies the error signal 80 , which is related in size and sign (positive or negative) to the difference between the actual output power signal 74 and the target output power signal 76 . If there is a large disparity between the actual output power and the target output power, the error signal 80 has a large value. If the actual output power is approximately equal to the target output power, the error signal 80 has a very small size or is essentially absent. The sign of the error signal 80 determines whether more or less power should be delivered in order to achieve the target power.

Details of the pulse width modulation circuit 82 , the driver circuit 86 , the power amplifier 22 and the power transformer 26 are shown in FIG. 3. The error signal 80 from the comparator 78 ( FIGS. 1 and 2) is applied to an integrator, which consists of an operational amplifier 134 and an integrating feedback circuit, which contains a capacitor 136 . The integrator causes error signal 80 to be continuously integrated over time and provides control loop stability. An output signal 138 of the integrator is always a trigger level signal of positive value. The sign of the error signal generated by the comparator 78 ( FIG. 2) is coordinated with the operation of the integrator to produce the positive level trigger level signal 138 . If the error signal 80 is negative in sign, indicating a need for more power, the integration increases the size of the trigger level signal 138 . If the error signal 80 is positive, which indicates a need for less power, the integration reduces the size of the trigger level signal 138 . If the error signal 80 is zero, the size of the trigger level signal 138 remains unchanged.

The trigger level signal 138 is applied to the base terminal of a transistor 140 . A transistor 142 and transistor 140 form a discrete comparator. The other input signal 144 of this discrete comparator is applied to the base terminal of transistor 142 . This other input signal 144 is the signal on a capacitor 146 . A transistor 148 and its associated biasing elements form a constant current source for charging the capacitor 146 at a constant current rate. Accordingly, the voltage signal across capacitor 146 rises linearly or in a ramped manner and thus generates a ramped or sawtoothed input signal 144 . An edge signal 150 from an edge detector 152 feeds a field effect transistor (FET) 154 to discharge the capacitor 146 . After capacitor 146 is discharged, it immediately begins to recharge.

Sawtooth signal 144 on capacitor 146 is periodic because edge signal 150 is periodic, and capacitor 146 periodically discharges through FET 154 . The periodic edge signal 150 is obtained from the oscillator signal 98 , which is supplied by an oscillator 156 provided as a pulse phase device, which is part of the driver circuit 86 . The oscillator signal 98 defines the frequency for the surgery signal 32 , which is supplied to the patient by the electrosurgery generator 10 . The oscillator signal 98 is shown in Fig. 4A. The edge detector 152 responds to each positive going and every negative going edge of the oscillator signal 98 and delivers a narrow pulse on every edge transition of the oscillator signal. The edge signal shown in FIG. 4D thus consists of a series of relatively narrow pulses, each of which occurs on one edge of the oscillator signal 98 . Each pulse of the edge signal causes the FET 154 to quickly discharge the capacitor 146 . The constant current source formed by transistor 148 immediately begins to charge capacitor 146 , and the voltage across the capacitor builds up linearly to produce sawtooth signal 144 , which is shown in FIG. 4E. The sawtooth signal 144 shown in FIG. 4E thus takes the form of a sawtooth wave, the frequency of which is determined by the edge signal 150 and is approximately twice the frequency of the oscillator signal 98 shown in FIG. 4A.

Oscillator signal 98 is applied to flip-flop logic and gate circuit 160 and to duty cycle generator 92 , as shown in FIG. 3. The duty cycle generator 92 is under the control of the mode logic circuit 62 ( FIG. 1) based on the signals 94 and sets the duty cycle signal 96 to control the delivery of the radio frequency pulses according to the selected mode. The duty cycle signal 96 is related to and coordinates with the oscillator signal 98 to cause the on and off periods of the duty cycle envelope to begin and end with the oscillator cycles. As long as the duty cycle generator 92 requires the surgical signal 32 to be supplied by the duty cycle signal 96 , the logic and gate circuit 160 supplies two periodic pulse phase signals 162 and 164 with the predetermined high frequency of the oscillator signal 98 . The two pulse phase signals are 180 ° out of phase with each other and are referred to as pulse phase 1 signal 162 and pulse phase 2 signal 164 . The width of each pulse in both pulse phase 1 and pulse phase 2 signals represents the maximum width to which each driver pulse 90 ( Figs. 1 and 3) may be made to achieve power control. The pulse phase 1 signal and the pulse phase 2 signal are shown in Figures 4B and 4C, respectively.

The technique of achieving pulse width modulation by the trigger level signal 138 will now be described. Initially, edge signal 150 causes FET 154 to discharge capacitor 156 . Then capacitor 146 begins to charge and transistor 142 begins to conduct. Transistor 142 continues to conduct when the voltage on capacitor 146 reaches a value that is equivalent to the value of trigger level signal 138 .

As soon as the voltage on capacitor 146 , ie sawtooth signal 144 , rises slightly above trigger level signal 138 , transistor 140 begins to conduct and transistor 142 ceases to conduct because the voltage at the base terminal of transistor 142 is the voltage at the base terminal of transistor 140 has exceeded. After transistor 140 begins to conduct, a termination signal 166 is present at resistor 168 and at the base of transistor 170 . The termination signal 166 is shown in Fig. 4G.

The effects of the trigger level signal 138 in controlling the sawtooth signal 144 due to the action of the discrete comparator device, which is formed by the transistors 140 and 142 , are illustrated in FIG. 4F. As soon as the sawtooth signal 144 rises to a value that is equivalent to the trigger level signal 138 , the termination signal 166 shown in FIG. 4G is provided. The width of each pulse of termination signal 166 is the remaining time portion of each interval of sawtooth signal 144 ( FIG. 4E) before capacitor 146 is discharged and the start of the next single sawtooth of the sawtooth signal. The high portion of termination signal 166 biases transistor 170 conductive.

Pulse width control signal 84 is generated by switching transistor 170 . The value of signal 84 drops immediately when transistor 170 begins to conduct because of the effects of resistor 174 . If transistor 170 is not conductive, the value of signal 84 is high. The pulse width control signal 84 is shown in Fig. 4H. The pulse width control signal 84 is the inversion of the termination signal 166 shown in FIG. 4G.

The pulse width control signal 84 is applied to an input terminal of two AND circuits 176 and 178 . Pulse phase 1 signal 162 is applied to the other input terminal of AND circuit 176 , and pulse phase 2 signal 164 is applied to the other input terminal of other AND circuit 178 . AND circuits 176 and 178 provide high output signals 180 and 182 , respectively, as long as both input signals are high. A pulse width modulated (PBM) phase 1 signal 180 is present in the presence of the pulse phase 1 signal 162 with the high signal value and in the presence of the pulse width control signal 84 with the high signal value. The pulse width modulated phase 1 signal 180 goes low when the pulse width control signal 84 drops to a low signal value. Accordingly, the time width of the pulse width modulated phase 1 signal 180 is controlled or modulated by the pulse width control signal 84 . This is illustrated by the fact that the signals shown in Figs. 4B and 4H are both at high signal levels during the time that the pulse width modulated phase 1 signal 180 shown in Fig. 4I is provided . Once the pulse width control signal 84 shown in FIG. 4H goes low, the pulse width modulated phase 1 signal 180 also goes low. A similar situation exists with respect to the pulse width modulated phase 2 signal 182 . AND circuit 178 samples pulse phase 2 signal 164 ( FIG. 4C) with pulse width control signal 84 ( FIG. 4H). The width of each pulse width modulated phase 2 signal 182 ends when the pulse width control signal 84 goes low. The pulse width modulated phase 2 signal is shown in FIG. 4J and is obtained according to FIGS . 4C and 4H in the logic type which is determined by the operation of the AND circuit 178 .

The edge signal 150 controls the FET 184 simultaneously with the FET 154 . When FET 184 is conductive, the value of signal 166 drops approximately to the reference value and transistor 170 ceases to conduct. Conduction of FET 184 thus ensures that pulse width control signal 84 begins at a high signal value every pulse width determination period and that transistor 142 is also conductive at the beginning of each pulse width determination period.

As described above, error signal 80 and trigger level signal 138 control the width of each pulse width modulated phase 1 and phase 2 signals 180 and 182, respectively. If the error signal 80 has a substantial magnitude in the negative direction, which indicates the need for high power, the sawtooth signal 144 ( FIG. 4E) will not reach the relatively large size of the trigger level signal 138 , in contrast to the situation shown in FIG. 4F. Therefore, essentially full-width pulse width modulated phase 1 and phase 2 signals 180 and 182 are provided because transistor 140 does not become conductive. Edge signal 150 will cause capacitor 146 to discharge, with transistor 140 becoming conductive at all. Because transistor 140 never becomes conductive, pulse width control signal 84 remains high and the width of each pulse of pulse width modulated phase 1 and phase 2 signals 180 and 182 becomes the full width of pulse phase 1 and pulse phases -2 signals 162 or 164 driven. Accordingly, FIGS . 4B and 4C also show the full width pulse width modulated phase 1 and phase 2 signals 180 and 182, respectively. As soon as the power builds up and the error signal 80 drops to zero, the signal value of the trigger level signal 138 reaches the target power setting because the width of the pulses is determined in such a way that the target power is delivered. If the electrosurgical generator 10 delivers excessive power, the error signal 80 becomes positive. The integration of the positive error signal 80 results in reducing the magnitude or signal value of the trigger level signal 138 , which causes the pulse width control signal 84 ( FIG. 4H) to decrease to a low signal value at an earlier point in every full phase period. Accordingly, the width of each pulse width modulated phase 1 and phase 2 signal is reduced, thereby reducing the size of the output power.

In addition to the functions of the flip-flop logic and gate circuit 160 described above, the flip-flop logic and gate circuit also includes gate circuit elements (not shown) which ensure that first the pulse width modulated phase 1 signal 180 and then the pulse width modulated phase 2 Signal 182 is supplied. In addition, when the duty cycle generator 92 requests the surgery signal 32 to be terminated, the logic and gate circuit 160 ensures that the duty cycle envelope on time ends after a pulse width modulated phase 2 signal has been provided. All functions of the flip-flop logic and gate circuit 160 can be achieved by interconnecting binary logic elements, mainly flip-flops and gates.

The pulse width modulated phase 1 and phase 2 signals 180 and 182 are each applied to their own phase driver circuit. A phase driver circuit 186 is shown. The phase driver circuits for the two pulse-width modulated phase 1 and phase 2 signals 180, 182 correspond to the single phase driver circuit 186 shown . Accordingly, the operation of the phase driver circuit 186 will now be described with reference to a pulse width modulated phase signal P, although the two pulse width modulated phase 1 and phase 2 signals 180, 182 have the same effect on their respective phase driver circuit as the phase signal P on the phase driver circuit 186 .

The phase signal P is applied to the phase driver circuit 186 at 188 and causes an FET 190 to become conductive. A transformer 192 has a center tapped primary winding, the coil 194 of which is polarized to produce a positive signal at terminal 196 with respect to terminal 198 and a positive signal at terminal 200 with respect to terminal 202 . Terminals 196 and 200 are connected to FETs Q1A and Q1B of power amplifier 22 . The positive signals at 196 and 200 turn on the two FETs Q1A and Q1B, causing current at 20 to be passed from the DC power supply 16 ( FIG. 1) through the primary winding of the power transformer 26 . Whenever the phase signal P ends, a narrow reset pulse on conductor 204 goes high. The reset pulse signal is generated by the negative going edge of the phase signal P. An FET 206 becomes conductive and current is temporarily passed in the reverse direction through a primary winding coil 208 of transformer 192 . The narrow reverse pulse of current in primary winding coil 208 resets the magnetization of the core of transformer 192 to make it ready for conduction during the next phase signal P. The various signals at terminals 196 , 198 , 200 and 202 illustrate those which together form driver signal 90 .

The other of the two pulse width modulated phase signals 180 , 182 has a corresponding effect on its phase driver circuit and the FETs Q2A and Q2B are made conductive and non-conductive in the same manner as described above. When the FETs Q2A and Q2B are conductive, the direction of current flow in the primary winding of the power transformer 26 is reversed. Accordingly, the pulse width modulated AC signal 28 is generated by the driver signal 90 applied to the amplifier 22 . Examples of the alternating pulse width modulated signal from the driver pulses 24 are shown in Figures 4K and 4L.

The alternating pulse width modulated signal on the primary winding of the power transformer 26 for full width driver pulses of the driver signal 90 is shown in FIG. 4K. In the transformer input signal shown in FIG. 4K, it should be noted that the full width pulse width modulated phase 1 signal (e.g. FIG. 4B) produces the positive part of this signal and that the full width pulse width modulated phase 2 signal (e.g. . 4C) is produced B. Figure the negative part of the transformer input signal. For less than full width driver pulses of driver signal 90 , the transformer input signal applied to the primary winding of power transformer 26 is shown in FIG. 4L. Again, the pulse width modulated phase 1 signal ( FIG. 4I) generates the positive part of the driver pulses 24 , whereas the pulse width modulated phase 2 signal ( FIG. 4J) generates the negative part of the driver pulses 24 . It can be seen that the drive pulses 24 of the PBM signal shown in FIG. 4L have exactly the same frequency characteristic as the oscillator signal 98 ( FIG. 4A).

The amount of energy provided by the AC pulse modulated signal 28 from the power transformer 26 is generally determined by the area above and below the zero line of the signals shown in FIGS . 4K and 4L, although the AC pulse modulated signal 28 is due to the inductive effects of the Filters 30 will not actually have the rectangular waveforms shown. This energy is presented on a periodic basis with the bandpass frequency of the bandpass filter 30 ( Fig. 1). Accordingly, the bandpass filter 30 is driven at its bandpass frequency to provide the sinusoidal surgery signal 32 shown in FIG. 4M at the predetermined radio frequency. The passive dummy elements of the bandpass filter 30 convert the AC pulse-modulated signal 28 into sinusoidal oscillations. Each period (vibration) of the sinusoidal surgery signal 32 is generated by a period (a positive and a negative drive pulse 24 ) of the pulse width modulated signal (e.g. FIGS . 4K and 4L) and results accordingly from this one period. The relationship and correspondence between the driver pulses 24 of the pulse width modulated signal and the sinusoidal surgery signal 32 results from a comparison of FIG. 4M with FIGS. 4K and 4L. When a full width pulse width modulated signal such as that shown in Fig. 4K is received, the amplitude of the sinusoidal surgery signal 32 will be greater than when a less than full width pulse width modulated signal as shown in Fig. 4L is at a load with the same impedance. Therefore, the power of the surgical signal 32 is determined by the width of the pulse width modulated phase 1 and phase 2 signals 180 , 182 and by the corresponding pulses of the driver signal 90 which control the switching of the amplifier 22 .

One of the advantages of controlling the output of DC power supply 16 by control signal 18 ( FIG. 1) and by pulse width modulation as described herein is that pulse width modulation achieves better resolution (ie, allows) for given power settings expanding to essentially the majority of the pulse width). The DC power supply 16 ( FIG. 1) thus generally or roughly regulates the size of the power, and the pulse width modulation technique described here achieves final, controlled and rapid control over the size of the power actually delivered. However, the intrinsic maximum power output capability of the power supply 16 is limited by this solution, and a relatively quick decrease in power occurs at higher output impedances.

Claims (13)

1. electrosurgery generator that provides a surgical signal ( 32 ) at a predetermined high frequency for performing a surgical procedure,
with a power supply ( 16 );
with a power amplifier ( 22 ) connected to the power supply ( 16 ) for supplying driver pulses ( 24 );
with an output stage ( 26 , 30 ) connected to the power amplifier ( 22 ), which receives the driver pulses ( 24 ) and emits the surgical signal ( 32 );
a setpoint generator ( 12 , 60 ) for providing a setpoint output signal ( 76 ) which is related to the setpoint output from the surgery signal ( 32 ); and
with a power control circuit with a current sensor ( 36 ) for sensing the actual current of the surgical signal ( 32 ), a voltage sensor ( 40 ) for sensing the actual voltage of the surgical signal ( 32 ), a multiplier ( 72 ) for multiplying a current sensing signal ( 38 ) and a voltage sensing signal ( 42 ) from the current sensor ( 36 ) or the voltage sensor ( 40 ) for generating an actual output power signal ( 74 ) and a comparator ( 78 ) for comparing the actual output power signal ( 74 ) with the desired output power signal ( 76 ) and for generating an error signal ( 80 ), which is related to the difference between these signals ( 74 , 76 ),
characterized in that the power control circuit has a pulse width modulation circuit ( 82 ) and a driver circuit ( 86 ),
that the pulse width modulation circuit ( 82 ) receives the error signal ( 80 ) and outputs a corresponding pulse width control signal ( 84 ) to the driver circuit ( 86 ), and
that the driver circuit ( 86 ) is connected to the power amplifier ( 22 ) in order to modulate the time width and therefore the energy content of each driver pulse ( 24 ) supplied by the power amplifier ( 22 ) in accordance with the pulse width control signal ( 84 ), so that the output stage ( 26 , 30 ) delivers each oscillation of the surgical signal ( 32 ) from the energy content of at least one driver pulse ( 24 ). 2. Electrosurgery generator according to claim 1, characterized in that the current sensor ( 36 ) and the voltage sensor ( 40 ) sense the actual current or the actual voltage of the surgery signal ( 32 ) directly at the output of the output stage ( 26 , 30 ). 3. Electrosurgery generator according to claim 1 or 2, characterized in that the setpoint generator ( 12 , 60 ) delivers at least one current limit signal ( 56 ) or a voltage limit signal ( 58 ) and
that the power control circuit has at least one limiting circuit ( 52 or 54 ) which receives the supplied current or voltage limit signal ( 56 or 58 ) and the corresponding current sensing signal ( 38 ) or voltage sensing signal ( 42 ) and the current or voltage limit signal ( 56 or 58 ) instead of the corresponding current or voltage sensing signal ( 38 or 42 ) to the multiplier ( 72 ). 4. Electrosurgery generator according to claim 3, characterized in that the current or voltage limit signal ( 56 , 58 ) received by the limiting circuits ( 52 , 54 ) has a constant value. 5. Electrosurgery generator according to claim 3, characterized in that the current or voltage limit signal ( 56 , 58 ) received by the limiting circuits ( 52 , 54 ) is in a linear relationship to the desired output power signal ( 76 ). 6. Electrosurgery generator according to claim 3, characterized in that the relationship between the current or voltage limit signal ( 56 , 58 ) received by the limiting circuits ( 52 , 54 ) and the desired output power signal ( 76 ) is non-linear. 7. Electrosurgery generator according to one of claims 1 to 6, characterized in that the power control circuit has a converter circuit ( 44 ) for converting the current sensing signal ( 38 ) into an effective current sensing signal ( 48 ) and that the power control circuit has a further converter circuit ( 46 ) for converting the Voltage sensing signal ( 42 ) into an effective voltage drop signal ( 50 ). 8. Electrosurgery generator according to one of claims 1 to 7, characterized in that the pulse width modulation circuit ( 82 ) contains:
an integrator ( 134, 136 ) which receives the error signal ( 80 ), integrates the error signal over time and generates a trigger level signal ( 138 ) which is related to the integrated value of the error signal,
means ( 146, 148 ) for generating a sawtooth signal having a periodic series of sawtooth vibrations occurring at a predetermined frequency which is related to the frequency of the driver pulses ( 24 ),
comparator means ( 140, 142 ) which receives the sawtooth signal and the trigger level signal ( 138 ) and generates the pulse width control signal ( 84 ) which occurs periodically at the predetermined frequency of the sawtooth signal and which controls the width of each driver pulse ( 24 ). 9. Electrosurgery generator according to one of claims 1 to 8, characterized in that the driver circuit ( 86 ) contains:
pulse phase means ( 156 ) for generating a pulse phase signal having a periodic series of phase pulses occurring at the frequency of the drive pulses ( 24 ) and
a gate circuit ( 160 ) which receives the pulse phase signal and the pulse width control signal ( 84 ) and generates each driver pulse ( 24 ) having a width related to the phase pulse signal. 10. Electrosurgery generator according to claim 9, characterized in that the width of each phase pulse defines the maximum possible width of each driver pulse ( 24 ). 11. Electrosurgery generator according to claim 9 or 10, characterized in that the gate circuit ( 160 ) initiates each driver pulse ( 24 ) upon the occurrence of each phase pulse and ends each driver pulse ( 24 ) in accordance with the pulse width control signal ( 84 ). 12. Electrosurgery generator according to one of claims 9 to 11, characterized in that the pulse phase device ( 156 ) generates a pulse phase 1 signal ( 162 ) and a pulse phase 2 signal ( 164 ) which are 180 ° out of phase with respect to one another , wherein both the pulse phase 1 signal and the pulse phase 2 signal have the properties of the pulse phase signal;
that the predetermined frequency of the sawtooth vibrations of the sawtooth signal and the frequency of the pulse width control signal ( 84 ) correspond to twice the frequency of the surgery signal ( 32 ); and
that the gate circuit ( 160 ) receives the pulse phase 1 signal and the pulse phase 2 signal and individual phase 1 driver pulses in relation to the phase 1 pulse signal and the pulse width control signal ( 84 ) and individual phase 2 driver pulses in Relation to the phase 2 pulse signal and the pulse width control signal ( 84 ) is generated, wherein the phase 1 driver pulses and the phase 2 driver pulses form a driver signal ( 90 ) from the driver circuit ( 86 ) to the power amplifier ( 22 ). 13. Electrosurgery generator according to claim 12, characterized in that the output stage ( 26 , 30 ), which receives the driver pulses ( 24 ) and generates each oscillation of the surgery signal ( 32 ), a half oscillation of the surgery signal ( 32 ) from a phase 1 driver pulse and generates the other half wave of the surgical signal ( 32 ) from a phase 2 driver pulse.